The objective for all error correction coding/decoding techniques is to provide, at the digital data receiver, an ability to correct errors introduced into the digital bit stream when the data is transmitted over a noisy communication channel. This objective may be accomplished by suitable encoding of the digital data stream by an error-correction coder prior to transmission over the channel. Then, at the receiver end of the communication channel, an error correction decoder is employed to map the received coded data back into the original information bit stream. If not too many errors occur in the channel, this decoding process at the receiver produces error-free data reception, even though some errors are introduced into the coded bit stream as it passes through the noisy communication channel.
Where the error correction coding scheme at the transmitter takes the form of a convolutional encoding technique, a decoding procedure, known as a Viterbi algorithm decoder, has been found to be particularly attractive for recovering the transmitted digital data from a receiver of a noisy bit stream. For an overview of the Viterbi algorithm attention may be directed to articles by A. J. Viterbi entitled "Error Bounds for Convolutional Codes and an Asymptotically Optimum Decoding Algorithm, IEEE Trans. Inform. Theory, Vol IT-13, pp. 260-269, April, 1967, and "Convolutional Codes and Their Performance in Communication Systems," IEEE Trans. Commun. Technol., Vol. COM-19, pp 751-722, October 1971 and an article by G. D. Forney entitled "The Viterbi Algorithm," Proc. IEEE, Vol. 61, pp 268-278, March 1973.
Of the signal processing techniques that have been developed to date for implementing the Viterbi Algorithm, all are essentially digitally based schemes, requiring the interfacing of a number of different functional components, resulting in a decoding system that is both costly and complicated. For an illustration of such proposals attention may be directed to the U.S. Pat. No. 4,015,238 to Davis; Clark et al U.S. Pat. No. 3,789,360; Melvin U.S. Pat. No. 4,087,752; and Acampora U.S. Pat. No. 4,087,707.